With reference to gas turbine members, engine members for aircraft, chemical plant materials, engine members for automobile such as turbocharger rotors, and high temperature furnace members, the strength is needed under a high temperature environment and an excellent oxidation resistance is sometimes required. A nickel-based alloy and cobalt-based alloy have been used for such a high-temperature application.
Many of the nickel-based alloys are strengthened by the formation of γ′-phase [Ni3(Al,Ti)] having an L12 structure. The γ′-phase gives excellent high temperature strength and high temperature creep characteristics because it has an inverse temperature dependence in which the strength becomes higher with rising temperature. The γ-phase becomes the nickel-based alloy suitable for heat-resistant applications such as rotor blades for gas turbine and turbine discs. On the other hand, the cobalt-based alloy is formed by using the solid solution strengthening and the precipitation strengthening of carbide. The system containing a large amount of chromium is excellent in corrosion resistance and oxidation resistance, and further has good wear resistance properties. Thus, it is used as a member, for example, a stator vane and a combustor.
Recently, the improvement of thermal efficiency in various heat engines is strongly required in order to improve fuel efficiencies and reduce the effects on the environment. The heat resistance required for heat engine components has been extremely demanding. For that reason, the development of a novel heat-resistant material as an alternative to the conventional nickel- or cobalt-based alloys has been examined.
With reference to novel heat-resistant alloys, many research reports have so far been published. In recent years, noble-metal materials such as Ir system and Pt system have been attracting a lot of attention (Nonpatent document 1). Both Ir and Pt exhibit good oxidation resistance, and further there is a report that an intermetallic compound such as Ir3Nb having the L12-structure which is the same as that of the γ′-phase of nickel-based alloy is used as a strengthening phase. (Patent document 2)
Nonpatent document 1: JOM, 56 (9), 2004, pp. 34-39
Patent document 2: JP-A 2001-303152